I considered taking it after completing my MSEE but never followed through. In retrospect, I wish I had as it's one of the few things that can go on a resume that means anything. Other things are degrees, patents and arguably publications. If you've been out of school a long time, I'd expect it would be difficult. After passing the PhD entrance exam, it would have been a piece of cake to handle any of the math and all the basic engineering stuff. I went back for my Masters through a program at my work, so could have taken the initial FE and then probably a year later taken the full PE exam, before all that math just dribbled out of my ears.
I've never needed the PE in the 33 years I've worked as an engineer, but I'm a EE. My son is going into his senior year as a civil engineer and will absolutely take it. If you're doing analysis and stamping prints to sign off a design, you legally have to have a PE license in your state. I don't know if it's still the case, but I worked at a company acquired by a Texas based company and there was a big uproar because at the time, to put "Engineer" on your card, you had to have your PE. Our company had long time legends in the field who didn't have their PE. The Texas company relented and decided that since none of us were based in Texas, we could put whatever we wanted on our cards. I considered Grand Pubah, but ended up using "Power Guy" since that's how the sales guys always introduced me anyways (I'm a power electronics designer).